Manually tuning a musical instrument can be a difficult and tedious process, usually requiring a considerable amount of time and skill. Frequently, a musician will need to verify or change the tuning of an instrument during a performance but, because of the time required, manually retuning the instrument is usually unacceptable. One common, although expensive and inconvenient, solution to this problem is to have properly tuned spare instruments available for such occasions. A much better solution is to have a system for tuning an instrument within a length of time short enough to be acceptable by an audience.
To satisfy this need, there are many different kinds of automatic tuning systems, which can be built into a stringed instrument. Such systems provide ease and convenience as well as accuracy in tuning an instrument, especially in front of an audience. However, these systems do not provide a musician with the capability of easily determining if the instrument is in tune without retuning. Also, these automatic systems are often only able to fine tune an instrument; that is, the instrument must be roughly tuned to within the operating range of the automatic system before the system will work.
Many different types of automatic tuning systems have been devised. There are open-loop systems which drive a tuning actuator to a predetermined position for each desired frequency. These have the advantage of being able to change tuning silently, and therefore unnoticed, during a performance. There are closed-loop systems which measure the frequency of the tone produced by the instrument, compare it to a desired value, and use the result of the comparison to control an actuator which tunes the instrument. This technique is accurate in that it directly controls the frequency of the instrument and is independent of other factors which affect frequency. However, it has the disadvantage that an audible tone must be produced while the instrument is being tuned and the audible tone may preclude tuning during a performance. Some tuning systems, because of interactions between strings, sequentially tune each string and then iterate to compensate for the interactions. Others tune selected strings, or all strings, simultaneously and then iterate. Still other systems measure the tension of (actually, the force applied to) a string and compare the measured value with a desired value to produce an actuator control signal.
A system which compensates for the effect of adjusting one string on the frequencies of the remaining strings, described in U.S. Pat. Nos. 4,803,908 and 4,909,126 to Skinn et al., both of which are herein incorporated by reference in their entirety, involves the use of a calibration function which relates the position of each actuator to the frequencies produced by all the instrument's strings. Creating the calibration function involves the measurement of frequencies at multiple positions of each actuator and, through regression techniques, relating the position of each actuator to not only the frequency of its own string but to the frequencies of the other strings as well. The use of regression techniques provides the advantage that a prior knowledge of the detailed characteristics of the instrument being tuned is not required. Also, the calibration function can be updated by recalibration as the instrument ages, or as environmental or other changes occur. Using a calibration function generated from the particular instrument being tuned permits open-loop, and therefore silent, tuning with accuracy comparable to that of closed-loop systems.
Automatic tuning systems usually have a transducer for generating an electrical signal representing the sound produced by the strings and a processor for obtaining the frequency of that signal. However, none of the previously described systems provides a display of all the frequencies simultaneously which can be used for manually tuning the instrument. If, for example, a string breaks and is replaced, or a new set of strings is installed, it is necessary even with an automatic tuning system to manually tune the instrument to a point within the operating range of the automatic system. Manually tuning an instrument under these conditions usually requires for reference a tone generator or another musical instrument, or else some kind of frequency measuring device. All of these tone references only reveal information about one string at a time. However, because the tensions in the individual strings interact, manually tuning a stringed instrument is much easier if the effects on all strings are evident at the same time.
There are many different types of devices, frequently called tuners, available for providing frequency information to the person tuning an instrument. One type of tuner has a microphone for detecting the audible tone produced by the string of an instrument and a meter or digital display for displaying the frequency of the tone to the person tuning the instrument. Another type of tuner is a tone generator for producing an audible reference tone to which a person can compare the frequency of a string of the instrument being tuned. Tone generators range from simple tuning forks to electronic devices producing a wide range of selectable frequencies. However, all these devices provide information about only one frequency at a time and typically are not a part of the instrument being tuned.
It is therefore an object of this invention to provide a display, indicating the frequencies of all the strings on an instrument either individually or simultaneously, which is available when a musician is playing or manually tuning the instrument. A further object of the invention is to enable a musician to quickly evaluate the tuning of an instrument and to tune the instrument manually to within the working range of the automatic tuning system.